Producing thin metal wire directly from molten metal is an inexpensive method of production. Moreover, the thin metal wire produced by this method is characterized by retaining the physical properties peculiar to the metal and, therefore, being suitable for use in electric and electronic parts, composite materials, and textile materials. Further, the metal wire can exhibit high tensile strength because of its small thickness. Therefore, the wire is a promising material in various industrial applications. If the thin metal wire obtained by being super-quenched possesses a circular cross section and an amorphous, non-equilibrium crystalline, or microcrystalline structure, it has a strong possibility of exhibiting numerous outstanding chemical, electromagnetic, and physical characteristics and finding practical utility in a host of fields. A number of methods have heretofore been developed for producing a thin metal wire of uniform quality at a low cost. One of these methods contemplates producing the thin metal wire in the same manner as the melt spinning of synthetic fibers currently adopted for mass production. The melt-spinning method for producing a thin wire of metal by drawing a metal in a molten state was developed by Pond et al. around 1958. This method has been studied in two versions; the staple method which comprises spouting molten metal through a spinning nozzle onto a rotary plate in motion and drawing the flow of molten metal with centrifugal force, and the continuous method which comprises spouting molten metal through a spinning nozzle into an atmosphere of inert gas and cooling the flow of molten metal into a continuous thin wire. The staple method produces a flat metal ribbon, which finds utility only in special applications as described in U.S. Pat. No. 2,825,108. The continuous method is utilized chiefly for metals of low melting points, because it requires a liquid metal of low viscosity to be cooled and solidified while the liquid metal is flowing with its continuity retained intact as described in U.S. Pat. Nos. 2,907,082 and 2,976,590.
In the meantime, a method of composite spinning which utilizes the spinnability of glass in producing a thin continuous wire by melt spinning a metal of high melting point is now under development. The methods described above, however, invariably entail too numerous problems to permit commercial production of a thin metal wire of high quality having a circular cross section at a low cost. A present conventional method for melt spinning of a metal wire will be described more specifically below.
Unlike a highly viscous molten substance such as of high molecular polymer, molten metal has extremely low viscosity and high surface tension. To produce a thin continuous wire from the molten metal by an ordinary melt spinning method, therefore, due consideration should be paid to the spouting speed and the solidifying speed of the flow of molten metal in connection with the two major factors, i.e., gravitational breakage and vibrational fracture in the spouted flow of molten metal. These problems are theoretically discussed in detail in Journal of Textile Society, Vol. 28, No. 1, page 23 (1972), for example. The most important question in this case, therefore, is how to lower the solidification limit which is liable to be inversely proportional to the difference between the temperature of the molten metal and that of the ambient air relative to the gravitational breakage limit which is liable to be proportional to the reciprocals of surface tension and specific gravity, namely, how to effect rapid cooling and solidification of the molten metal. Methods which are directed to stabilizing an extremely unsteady flow of molten metal spouted out of the spinning nozzle have also been proposed to the art. Japanese Patent Publication No. 24013/70, for example, discloses a method which, as a measure for stabilizing the flow of molten metal for the sake of cooling and solidifying activities, comprises spinning the molten metal into an atmosphere of a gas reactive with the metal thereby causing formation of a film of oxide or nitride on the surface of the thin flow of molten metal. A careful study of this method, however, reveals that it is extremely difficult for the molten metal to be stabilized so perfectly as though in a solidified state solely by the formation of such a film. Even when the film is formed, the molten metal is discontinuously deformed by virtue of gravitational attraction. Thus, the formation of the film hardly keeps pace with the constant renewal of the surface of the molten metal. In an extreme case, the flow of molten metal may have portions covered with a perfectly formed film and portions either covered with an insufficiently formed film or not covered at all, imparting detestable uniformity to the produced thin metal wire or causing fracture and breakage in the flow of molten metal. Worse still, this method only permits use of specific metals which are capable of forming a film of oxide or nitride.
Japanese Patent Application (OPI) Nos. 56560/73 and 71359/73 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") also suggest methods which spout the molten metal into a dense aggregate of froths or into a mass of bubbles and effect cooling and solidification of the flow of molten metal. These methods fall short of amply stabilizing the flow of molten metal because their cooling and solidifying speeds are quite slow. Recently, the so-called liquid quenching method which produces a uniform, continuous thin metal wire by causing the flow of molten metal spouted out of the spinning nozzle to come into contact with the surface of a solid roll rotating at a high speed before the molten metal sustains gravitational breakage or vibrational fracture thereby quenching and solidifying the molten metal at a high speed has been studied and proposed in various versions. Since this method provides the cooling at an extremely high speed of about 10.sup.5 .degree. C./seconds, it proves to be a highly advantageous method for stably producing a metal ribbon of high quality having an amorphous, nonequilibrium crystalline, or microcrystalline structure. Unfortunately, this method only produces a metal wire of flat faces, which finds utility only in special applications. This method, therefore, is incapable of producing a thin metal wire having a circular cross section.
Japanese Patent Application (OPI) No. 135820/79 (corresponding to U.S. Pat. No. 3,845,805) discloses a method which, for the purpose of producing a thin metal wire having a circular cross section, causes the flow of molten mettal to be passed through a quenching zone formed of a liquid medium and, consequently, effects solidification of the molten metal. The essential requirements for this invention are (1) that, in the quenching zone, the flow of molten metal just spouted out of the spinning nozzle and that of the liquid cooling medium are parallel to each other and (2) that the relative speed between the flow of molten metal spouted out of the spinning nozzle and that of the liquid cooling medium relies on the speed of the gravitational fall of the liquid cooling medium. Thus, the speed is 180 m/min. at best and cannot be increased any more. By this method, therefore, the speed of quenching and solidification cannot be easily increased.
The largest disadvantage of this method resides in the fact that since the flow of the liquid cooling medium is caused by its own gravitational fall, the disturbance consequently produced in the flow of the liquid cooling medium cannot be easily controlled. This disturbance in the flow of the liquid cooling medium is aggravated when the speed of the liquid cooling medium is increased. When the flow of molten metal is brought into contact with the liquid cooling medium in such heavy disturbance to be quenched and solidified, there are barely produced short lengths of thin metal wire heavily lacking uniformity of diameter and abounding in deformation. Thus, this method has no practicability. To obtain a thin metal wire of high quality and high performance having an amorphous, non-equilibrium crystalline, or microcrystalline structure, the flow of molten metal must be quenched and solidified at a cooling speed of not les than 10.sup.4 .degree. C./second. In this method, the cooling speed is not sufficient because the molten metal and the liquid cooling medium are flowing parallelly to each other at an equal, low speed within the quenching zone. Thus, this method cannot produce a thin metal wire of high quality having a circular cross section and an amorphous, non-equilibrium crystalline, or microcrystalline structure. Further, since the liquid cooling medium flows at a slow speed, it possesses a small kinetic energy. The liquid cooling medium itself and the surface thereof, therefore, are disturbed by the collision of this medium with the flow of molten metal spouted through the spinning nozzle and by the boiling, vaporization, and convection of the liquid medium, making it impossible to produce a thin metal wire of high quality having a circular cross section.
Japanese Patent Application (OPI) No. 69430/76 discloses a method which, in bringing the flow of molten metal into contact with the liquid cooling medium thereby effecting cooling and solidification of the molten metal for the purpose of producing a continuous thin metal wire having a uniform, circular cross section, limits the angle of contact between the liquid cooling medium and the flow of molten metal spouted out of the spinning nozzle to below 20.degree. and fixes the flow speed, V (m/min), of the liquid cooling medium within the range of V.sub.M &lt;V.ltoreq.5/2V.sub.M (wherein V.sub.M denotes the speed (m/min) of the flow of molten metal spouted out of the spinning nozzle). This method is advantageous for the purpose of minimizing the collision between the flow of molten metal and that of the liquid cooling medium and producing a continuous thin metal wire having a uniform, circular cross section. This method, however, falls short of providing perfect control of the disturbance in the flow of the liquid cooling medium. Since the angle of contact between the flow of molten metal and that of the liquid cooling medium is small, the cooling speed obtained at all by this method is not sufficient for a metal which is capable of forming an amorphous, non-equilibrium crystalline, or microcrystalline structure when cooled at a sufficiently high speed. By this method, therefore, it is difficult to produce a thin metal wire having an amorphous, non-equilibrium crystalline, or microcrystalline structure and, therefore, excelling in chemical, electromagnetic, and physical properties. Similarly to the method taught by the aforementioned Japanese Patent Application (OPI) No. 135820/74 (corresponding to U.S. Pat. No. 3,845,805), this method has a disadvantage that the liquid cooling medium is disturbed when the flow speed thereof is increased.
Japanese Patent Application (OPI) No. 64948/80 teaches a so-called rotary liquid spinning method which cools and solidifies the flow of molten metal spouted out of the spinning nozzle by introducing this flow of molten metal into a rotary member containing a liquid cooling medium. In this method, the flow of the liquid cooling medium is stabilized by virtue of centrifugal force even when the flow speed of the medium is increased and the cooling medium provides cooling of the molten metal at a high speed. This method, therefore, proves to be advantageous for the purpose of producing a thin metal wire of high quality having a circular cross section in a small lot. This method, however, maintains the layer of liquid cooling medium within the rotary member cylinder and collects the cooled and solidified thin metal wire continuously as wound up on the inner wall of the rotary cylinder. Consequently, the depth of the layer of liquid cooling medium, the windup speed, the temperature of the liquid cooling medium, etc., are varied. The present method, accordingly, entails too many problems to permit effective continuous, mass production of a thin metal wire of uniform quality. Further, this method must be worked out in a batchwise operation by all means because the rotary cylinder has rigidly limited inner volume and width. It is extremely difficult for this method to be carried out in a continuous operation on a commercial scale. This method by nature necessitates installation of one rotary cylinder for each spinning nozzle in use and, therefore, tends to call for huge cost for equipment and power supply.